This proposal is submitted in response to PA-04-119. It encompasses two priority research areas: "biology of arthropod vectors" and "natural history of infection". It builds upon our groups unusual expertise on chikungunya virus (CHIKV), a virus that has recently caused over 255,000 human cases in La Reunion, over 100,000 cases in India, and disease in tourists returning from the endemic area to Europe and China. The potential for secondary spread and establishment of a transmission cycle involving Aedes albopictus and Ae. aegypti is a credible threat and must be treated seriously (Pearson, 2006). The long-term goal of this research is to identify the mechanism underlying the binding of viral glycoproteins to mosquito midgut cells and investigate how these interactions determine/enhance viral infection in, and transmission by mosquitoes. This knowledge may facilitate antiviral strategy development. Central Hypothesis: viral genes determine the interactions of CHIKV and midgut cell surface proteins that promote transmission of the epidemic strain LR2006 OPY1 2005 by Ae. aegypti and Ae. albopictus mosquitoes. Aim 1: To determine and compare oral infectious dose 50 (OID50)s and infection dynamics of the epidemic strain CHIKV LR2006 OPY1 obtained from La Reunion and of a Central African strain SG41855, in Ae. aegypti and Ae. albopictus mosquitoes. Hypothesis: the unusual virulence and magnitude of the current outbreak of CHIKV in the Indian Ocean is due to changes in the viral genome that cause enhanced infection in, and transmission by mosquitoes. Aim 2: To develop infectious clones which express EGFP and to develop a replicon system to aid in the determination of sites of CHIKV infection in Ae. aegypti and Ae. albopictus mosquitoes. Infectious clone technology will provide important tools to examine alphavirus and mosquito interactions at the molecular level. Aim 3: To identify putative cell surface receptor proteins in Ae. aegypti mosquitoes for CHIKV that can modulate CHIKV mosquito infectivity. Hypothesis: suppression of CHIKV-binding cell surface proteins expression levels in Ae. aegypti results in a decreased infection and dissemination. Innovation, outcomes, and benefits: This study will provide much needed background information on CHIKV from the current epidemic, and will allow us to generate tools and protocols required to further examine the mechanisms of mosquito-viral interactions. Fauci et al., (2005) highlighted the importance and value of research related to emerging infectious diseases, and chikungunya virus (CHIKV) is an excellent example of the substantial public health impact that a re-emerging virus can have. The ongoing epidemic of chikungunya has already caused over 255,000 human cases in the Indian Ocean island of La Reunion (>30% of the total population) and over 100,000 cases in India. The proposed research will investigate the mechanism of mosquito infection, identify mosquito midgut proteins that bind to CHIKV, and utilize a double-stranded RNA approach coupled with new molecular tools to evaluate infection, and dissemination dynamics of CHIKV in mosquitoes.